In 1989 approximately 700 million pounds of polyethylene terephthalate (PET) were consumed to produce soft drink bottles. Presently about 28% of this material is recycled with the remainder being placed in landfills or incinerated. Due to problems with overloaded landfills and the negative environmental image plastics has received recently, bills have been introduced aimed at establishing bottle deposits and the number of curbside recycling programs has increased tremendously. The collection of PET bottles and food trays through these programs has resulted in a source of post consumer PET which has been used for a number of applications. Generally these applications involve the conversion and fabrication of the post-consumer PET into materials of lower value. Examples of such applications are polyols for unsaturated polyesters or polyurethanes, fiberfill, carpet fibers, and strapping. Recycled PET is also blended with other materials such as polybutylene terephthalate, polycarbonate, or glass fibers, etc., for automotive as well as other engineering applications.
Post-consumer PET can also be recycled into resin which can be used in manufacturing containers for foods and beverages, such as carbonated beverage bottles. In such procedures, the post-consumer PET is generally depolymerized to oligomers or its monomers which are subsequently utilized as a raw material in the preparation of the recycled PET resin. Such a procedure for depolymerizing PET is described in U.S. Pat. No. 3,703,488 and U.S. Pat. No. 3,884,850.
In such recycling programs, it is important to separate the post-consumer PET from other plastics in the recycle stream. Foreign materials can be removed from such post-consumer PET feed stream by hand separation. Foreign materials, such as other plastics, can also be removed from the post-consumer PET feed stream by flotation procedures which are based upon density and/or wettability differences between the plastics. Nevertheless, such procedures generally do not result in the total removal of foreign materials from the post consumer PET feed stream. This is particularly true of glues, small particle size foreign materials, and polymeric melt blends. For instance, some post-consumer PET sources are melt blends of the PET with one or more other plastics. In the case of such melt blends, the other plastics cannot be removed from the PET by physical separation procedures. For instance, dual ovenable trays which are used extensively by the frozen prepared food industry typically contain about 97% PET and about 3% linear low density polyethylene. It is, of course, not possible to separate the polyethylene from the PET in such melt blends by mechanical means. Nevertheless, there is a tremendous need to remove polyethylene and other foreign materials which are intimately mixed with the PET from such feed streams.